SK3 channel expression during pregnancy is regulated through estrogen and Sp factor-mediated transcriptional control of theKCNN3gene

Abstract

Overexpression of the small-conductance calcium-activated K(+) channel 3 (SK3) in transgenic mice compromises parturition, suggesting that the SK3 channel plays a role in pregnancy. In wild-type mouse myometrium, expression of SK3 transcript and protein is significantly reduced during pregnancy, but the mechanism(s) responsible for this attenuation of channel expression is unknown. The promoter region of the SK3-encoding mouse KCNN3 gene contains two binding sites for specificity protein (Sp) transcription factors, two of which are expressed in the uterus: Sp1, which enhances gene transcription in response to estrogen; and Sp3, which competes for the same binding motif as Sp1 and can repress gene expression. We investigated the hypothesis that Sp1 and Sp3 regulate SK3 channel expression during pregnancy. In mouse myometrium, Sp1 expression was reduced during late gestation, whereas Sp3 expression levels were constant throughout pregnancy. Using a reporter system, we found that Sp1 overexpression resulted in a significant increase in SK3 promoter activation and that Sp3 cotransfection reduced promoter activation to basal levels. These findings indicate that Sp3 outcompetes Sp1 to decrease SK3 transcription. To determine whether high levels of estrogen in vivo can affect the regulation of SK3 protein levels by Sp factors, ovariectomized mice were implanted with a 17β-estradiol or placebo pellet for 3 wk; estrogen-treated mice had reduced uterine SK3 protein expression compared with placebo-treated counterparts. In human myometrial cells overexpressing Sp1, estrogen treatment stimulated expression of the SK3 transcript. Overall, our findings indicate that Sp1 and Sp3 compete to regulate SK3 channel expression during pregnancy in response to stimulation by estrogen.

Gestational Hypoxia Increases Reactive Oxygen Species and Inhibits Steroid Hormone–Mediated Upregulation of Ca 2+ -Activated K + Channel Function in Uterine Arteries

“…18,28 Estrogen has been shown to control SK Ca channel expression in human myometrial cells via the specificity protein family of transcription factors. 29 Although this significant, albeit small, change in SK3 channel expression may contribute to the channel function, the finding of the acute effect of NAC in the present study suggests that chronic hypoxia (either in vivo or ex vivo for 48 hours)–mediated ROS persist and predominately affect K Ca channel activities in the uterine arteries.…”

Estrogen Regulates the Expression of Small-Conductance Ca²⁺-Activated K⁺ Channels in Colonic Smooth Muscle Cells

“…Previous studies reported that estrogen elevated the SK3 mRNA expression in the rostral basal hypothalamus [10], endometrial epithelial cells [11], and myometrial cells [12]; furthermore, the overexpression of SK3 channels has been shown to dampen uterine contractility [13]. Therefore, we mainly focused on the effect of E2 on SK3.…”

“…The existence of functional SK2 in human and mouse cardiac myocytes has been reported, and genetic knockout of SK2 results in a delay in cardiac repolarization and atrial arrhythmias [32]. Functional SK3 channels are associated with a variety of smooth muscle tissues, such as the smooth muscle of blood vessels [33], bronchus [34], bladder [35], and uterus [12]. Moreover, SK3 channels participate in the purine-induced inhibition of colonic smooth muscle contraction [36].…”

“…Therefore, the relationship between estrogen and SK3 channels at the cellular level is of particular interest. Previously published data have shown that E2 can regulate the SK3 gene expression in central neurons [10] and myometrial cells [12]. Pierce et al [13] found that the force produced by uterine strips from SK3 T/T mice (overexpression of SK3 channels) was significantly less than that measured in uterine strips from WT (wild type) or SK3 DOX (SK3 knockout control) mice.…”

“…Apamin-sensitive SK channels are activated by 17β-estradiol (E2) in gonadotropin-releasing hormone (GnRH) neurons [9]. Estrogen elevates the SK3 mRNA expression in the rostral basal hypothalamus [10], endometrial epithelial cells [11], and myometrial cells [12]. Furthermore, the overexpression of SK3 channels dampens uterine contractility [13].…”